Ancient India in 300 BC may have had a population in the range 100–140 million. It has been estimated that the population was about 100 million in 1600 and remained nearly static until the late 19th century. It reached 255 million according to the first census taken in 1881.[12][13]
Studies of India's population since 1881 have focused on such topics as total population, birth and death rates, growth rates, geographic distribution, literacy, the rural and urban divide, cities of a million, and the three cities with populations over eight million: Delhi, Greater Mumbai (Bombay), and Kolkata (Calcutta).[14]
Mortality rates fell in the period 1920–45, primarily due to biological immunization. Other factors included rising incomes, better living conditions, improved nutrition, a safer and cleaner environment, and better official health policies and medical care.[15]